The present application relates to a molding apparatus, and to a pressure control mechanism for the molding apparatus. Specifically, the present application relates to injection molding machines which use tie bars to prevent twisting of the platens and to a pressure control mechanism for applying pressure to the platens.
It is well known to provide injection molding machines with tie bars, and means are generally provided to grip those tie bars to allow for the platens to withstand the high pressures applied to mold halves. Examples of machines with clamping or gripping mechanisms for the tie bars include U.S. Pat. Nos. 5,275,550, 5,620,723, 5,624,695, 5,645,875, and 4,874,302. Injection molding machines with similar features are also described in Brazilian Patent No. 9300002-2, German Patent No. 4230824, and European Patent No. 0747197.
Alternative arrangements of gripping mechanisms for injection molding machine tie bars are described in GB-A-2064415, DE-A-3034024, and East German Patent No. 133635.
It is an object of the present invention to provide a new pressure control mechanism for applying pressure to a platen of a molding machine.
According to a first aspect of the present invention a pressure control mechanism for applying pressure to a platen of a molding machine is provided the pressure control mechanism comprising a piston having a longitudinally extending bore therethrough for receiving a tie rod of the molding machine, the piston also having a front pressure applying surface, and a second, rear surface spaced longitudinally from said front surface, the pressure control mechanism further comprising a gripping mechanism supported by the piston, wherein said gripping mechanism comprises a substantially cylindrical body having a longitudinally extending bore therethrough, and a front support surface which is affixed to the rear surface of the piston such that the bores in the piston and said substantially cylindrical body are aligned, wherein said gripping mechanism further comprises a pair of gripping jaws mounted in said substantially cylindrical body to be movable relative to one another transversely of the longitudinal extent of the bore in the substantially cylindrical body; and moving means arranged to cause a relative movement of said gripping jaws towards one another to thereby grip a tie bar extending through said aligned bores, wherein said moving means comprises a rotatable disc, and movement translation means arranged to translate rotation of said disc into transverse movement of said gripping jaws.
Although a pressure control mechanism according to the present invention may be used in any molding machine where the piston is employed to actively pressurize the platen, the present invention has been specifically designed for use in injection molding machines where the piston must withstand the high pressures applied to the platen during the molding process.
In an embodiment of a pressure control mechanism according to the present invention the piston and the gripping mechanism are fixed together to form a single unit.
In a preferred embodiment of the present invention, the gripping jaws are mounted in recesses in said cylindrical body such that said recesses permit transverse sliding movement of the gripping jaws with respect to a longitudinal bore formed in said cylindrical body. The movement translation means comprise slots in one of the gripping jaws and said disc, and corresponding projections carried by the other of said disc and said gripping jaws, such that upon rotation of the disc each projection is moved along its corresponding slot to cause transverse sliding movement of said jaws. Preferably, each of said slots has an elongated, cranked shape. In a preferred embodiment of the present invention, the projections are carried by the disc, and each gripping jaw has a slot in which a corresponding projection is slidably received. Preferably, the projections are pins or rollers which extend generally in the longitudinal direction.
The construction according to the present molding apparatus is relatively simple and robust and avoids complex linkages between the piston and the gripping mechanism as are apparent in prior art constructions.
In another embodiment of the present invention, each gripping jaw has a concave gripping surface which extends over a segment of a circle having a similar radius to that of the longitudinal bore extending in said substantially cylindrical body. Preferably, a series of gripping formations are provided on the concave gripping surface of each said gripping jaw. These gripping formations may comprise a plurality of teeth or screw threads. For example, a series of gripping formations are provided on the concave gripping surface of each of said gripping jaws. In an embodiment, in each gripping mechanism, the rotatable disc of the moving means is supported for rotation within a retaining ring, the retaining ring being fixed to a rear support surface of said substantially cylindrical body, said rear support surface being longitudinally spaced from the front support surface thereof.
In yet another embodiment of the present invention, said moving means incorporates a rotatable disc which is structured and arranged to be rotated within a retaining ring. The retaining ring is coupled to a rear support surface of said substantially cylindrical body and the rear support surface is longitudinally spaced from the front support surface thereof.
Preferably, said moving means further comprises link means interconnecting the retaining ring and the rotatable disc. The link means are extensible and retractable in order to effect rotation of said rotatable disc.
The present invention also relates to a molding apparatus having a first and a second relatively movable platen, each of said movable platens carrying a respective mold half; tie rods extending between and through each of the first and second platens for guiding their relative movement; and controllable displacement means for causing relative movement between the first and second platens to open and close the mold halves.
The molding apparatus further comprises a pressure control mechanism for applying a pressure to each of the movable platens and to maintain them closed. The pressure control mechanism comprises a respective piston and cylinder unit associated with each tie rod, the piston of each of said units having a longitudinal bore through which an associated tie rod extends, and wherein the piston of each said units supports a gripping mechanism arranged to selectively grip the associated tie rod, wherein each of said gripping mechanisms is mounted for reciprocating movement together with its supporting piston. Each of said gripping mechanisms comprises a pair of gripping jaws arranged to be transversely movable with respect to the associated tie rod to selectively grip the tie rod; moving means arranged to cause relative movement of said gripping jaws towards one another in order to grip the associated tie rod. Each of said moving means comprises a rotatable disc; and movement translation means arranged to translate rotation of said disc into transverse movement of said gripping jaws.
While the piston in a molding apparatus according to the present invention may be used to actively pressurize the movable platens towards their closed position, it is generally preferred that the piston be used to withstand the high pressures applied to the platens during a molding process, and in particular to an injection molding process.
In an embodiment of the molding apparatus according to the present invention, the gripping mechanism and supporting piston are structured and arranged to be movable as a single unit. Preferably, in each gripping mechanism, said gripping jaws are mounted in recesses in said cylindrical body for transverse sliding movement with respect to the associated tie rod, and wherein said movement translation means comprise slots in one of the gripping jaws and said disc; and corresponding projections carried by the other of said disc and said gripping jaws, such that upon rotation of the rotatable disc each projection is moved along its corresponding slot (i.e., an elongated cranked shape) to cause a transverse sliding movement of said jaws. In a preferred embodiment, in each gripping mechanism, the projections are carried by the rotatable disc, and each gripping jaw has a slot in which a corresponding projection is slidably received. Preferably, said projections are pins or rollers which extend generally in the longitudinal direction.
In yet another preferred embodiment, the molding apparatus further comprises a single common drive means structured and arranged to drive the moving means of all of said gripping mechanisms; and link means linking all, of the gripping mechanisms to said single common drive means.
It is a particular advantage of the present invention to have a single common drive means as this reduces, for example, the number of hydraulic actuators required thereby reducing the manufacturing cost of the molding machines. For example, the single common drive means may be a hydraulic piston and cylinder unit.
Preferably, the link means interconnect the moving means of each gripping mechanism to the moving means of one or more of the other gripping mechanisms, and said single common drive means is connected to directly drive the moving means of one of the gripping mechanisms. As such all of the moving means are simultaneously driven by said single common drive means and the link means interconnecting the moving means of each gripping mechanism and one or more of the other gripping mechanisms.
In another embodiment of the molding apparatus according to the present invention, the piston of each of said piston and cylinder units has a first front surface for applying a pressure, and a second rear surface, spaced longitudinally from said front surface. The associated gripping mechanism comprises a substantially cylindrical body having a front support surface which is affixed to the rear surface of the piston, and a longitudinally extending bore therethrough which is aligned with the bore of the piston such that the associated tie rod extends through both the piston and the substantially cylindrical body. The pair of gripping jaws of said gripping mechanism are then mounted in said substantially cylindrical body in order to be movable relative to one another and transversely movable with respect to the associated tie rod.
Preferably, the moving means further comprises link means interconnecting said retaining ring and said rotatable disc. The link means is extensible and retractable in order to effect rotation of said disc and wherein the link means of each gripping mechanism is connected to the link means of one or more of the other gripping mechanisms.
In another preferred embodiment of the present invention, the molding apparatus further comprises adjustment means structured and arranged to adjust a longitudinal position of each tie rod relative to the first and second movable platens.